Unbeknownst to Celebrimbor, his partner in crafting the Rings was actually Sauron. The Dark Lord had come in the guise of wise Annatar to corrupt the Elves through the Rings of Power. By Second Age 1697, Sauron had learned that he could not control either the Elves nor the Dwarves through the Rings and led a large army towards Eregion. There he slaughtered Celebrimbor and scattered the people of Ost-in-Edhil. In response Durin sealed the Doors of Durin from the outside world.